The human brain is an exceedingly complex processing system, which integrates continual streams of incoming sensory input data with stored memories, uses the input data and memories in complex decision processes at both conscious and unconscious levels and, on the basis of these processes, generates observable behaviors by activation of its motor or movement control pathways and the muscles which these innervate. The neurons of the nervous system propagate input data by generating characteristic electrical pulses called action potentials (APs), or neural spikes, that can travel along nerve fibers. A single neuron or a group of neurons represent and transmit information by firing sequences of APs in various temporal patterns. Information is carried in the AP arrival times.
In certain cases of traumatic injury or neurological disease, the brain can be partially isolated from the periphery. Input data from certain senses are thus lost, at least for a portion of the body, as are many voluntary movements. Spinal cord injury is a well-known example of traumatic injury. With spinal cord injury, the pathways that link higher motor centers in the brain with the spinal cord and that are used for control of voluntary movements can be functionally transected at the site of the injury. As a result, the patient is paralyzed, and can no longer voluntarily activate muscles that are innervated by regions of the spinal cord below the level of the injury. Despite the injury to their long fibers, however, many of the cells in these higher brain regions that control voluntary movement will survive and can still be activated voluntarily to generate electric signals for controlling voluntary movement. By recording the electrical activities produced from these cells with implantable neural sensors (e.g., a microwire electrode array, a microwire, a magnetic field detector, chemical sensor, or other neural sensor), signals generated by the cells can be “exteriorized” and used for the control of external prostheses, such as an assist robot or an artificial limb, or functional electrical stimulation of paralyzed muscles. Additionally, these generated signals can be used for control of computer operations such as the movement of a cursor on a computer display.
Technology is now emerging that will allow prosthetic limbs to be controlled directly and unconsciously by the brain. If the brain signals normally used for controlling limbs can be harnessed, they can be used to control “neuroprosthetic” limbs. The technology required for interfacing recording hardware into the brain is known as the brain-machine interface (BMI). For BMIs to be effective, they must wirelessly transmit neural information to a processor that controls the prosthesis. Since information content scales with the number of recorded neurons, it is desirable to increase the number of electrodes that the BMI can monitor. However, limitations in available wireless technologies restrict the number of neural electrodes that can be monitored simultaneously.
Based on the above limitations in neural action potential signaling, it is desired to provide improved systems and methods for transmitting a signal indicating detection of a neural action potential. It is also desirable to provide improved technology for increasing the number of electrodes that can be monitored. Further, it is desirable to compress the useful neural signal data prior to transmission.